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United States Patent |
6,124,982
|
Usui
|
September 26, 2000
|
Zoom lens
Abstract
This specification discloses a zoom lens which has, in succession from the
object side, a first lens unit of positive refractive power, a second lens
unit of negative refractive power for focal length change, a third lens
unit for correcting the changing of an imaging plane resulting from a
focal length change, and a fourth lens unit of positive refractive power,
and in which an aspherical surface AS1 is provided on at least one lens
surface constituting the first lens unit and satisfying 1.65<hw/ht and
1.15<hw/hz, where ht is the maximum incidence height of an on-axis light
beam, hw is the incidence height of an off-axis light beam of a maximum
angle of view at the wide angle end, and hz is the incidence height of the
off-axis light beam of a maximum angle of view at a zoom position at a
variable power ratio Z.sup.1/4, and the power disposition and achromatism
condition of the first lens unit, a focusing system, etc. are
appropriately set.
Inventors:
|
Usui; Fumiaki (Utsunomiya, JP)
|
Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
Appl. No.:
|
110690 |
Filed:
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July 7, 1998 |
Foreign Application Priority Data
Current U.S. Class: |
359/686; 359/676; 359/683; 359/687; 359/688 |
Intern'l Class: |
G02B 015/14 |
Field of Search: |
359/676,683,686,687,688
|
References Cited
U.S. Patent Documents
5737128 | Apr., 1998 | Usui | 359/686.
|
5745300 | Apr., 1998 | Usui et al. | 359/684.
|
5751497 | May., 1998 | Usui et al. | 359/687.
|
Foreign Patent Documents |
6-242378 | Sep., 1994 | JP.
| |
Primary Examiner: Epps; Georgia
Assistant Examiner: Letendre; Suzanne
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Claims
What is claimed is:
1. A zoom lens having, in succession from the object side, a first lens
unit of positive refractive power, a second lens unit of negative
refractive power for focal length change, a third lens unit for correcting
the changing of an imaging plane resulting from a focal length change, and
a fixed fourth lens unit of positive refractive power, characterized in
that said first lens unit has a front lens sub-unit of negative refractive
power fixed during focusing, an intermediate lens sub-unit movable along
the optical axis thereof for focusing, and a rear lens sub-unit of
positive refractive power fixed during focusing, and when the variable
power ratio of said zoom lens is Z and the maximum incidence height of an
on-axis light beam in the first lens unit is ht and the maximum incidence
height of an off-axis light beam of a maximum angle of view at the wide
angle end in the first lens unit is hw and the maximum incidence height of
the off-axis light beam of a maximum angle of view at a zoom position at a
variable power ratio Z.sup.1/4 is hz, at least one lens surface at a
position satisfying 1.65<hw/ht and 1.15<hw/hz is made into an aspherical
surface AS1.
2. The zoom lens of claim 1, characterized in that said aspherical surface
AS1, when provided on a positive refracting surface, forms a shape in
which positive refractive power becomes stronger toward the peripheral
portion of the lens, and when provided on a negative refracting surface,
forms a shape in which negative refractive power becomes weaker toward the
peripheral portion of the lens, and when the combined focal length of said
first lens unit in a state in which it is in focus on an object at
infinity is f1 and the aspherical amounts at 100%, 90% and 70% of the
effective diameter of the lens on which said aspherical surface AS1 is
provided are .DELTA.10, .DELTA.9 and .DELTA.7, respectively, said
aspherical surface AS1 satisfies the following conditions:
##EQU4##
3. The zoom lens of claim 1, characterized in that said front lens sub-unit
is comprised in succession from the object side, of at least two negative
lenses and at least one positive lens, the negative lens most adjacent to
the object side forms a meniscus shape having its sharp concave surface
facing the imaging plane side, and when the average of the Abbe numbers of
said at least two negative lenses is .DELTA..nu.11n and the Abbe number of
said positive lens is .DELTA..nu.11p, said front lens sub-unit satisfies
the following condition:
19<.DELTA..nu.11n-.DELTA..nu.11p.
4. The zoom lens of claim 1, characterized in that said intermediate lens
sub-unit comprises at least one positive lens movable toward the imaging
plane side during focusing on an object at infinity to an object at a very
close distance and having a shape having its sharp convex surface facing
the imaging plane side.
5. The zoom lens of claim 1, characterized in that said rear lens sub-unit
is comprised of at least one negative lens and at least three positive
lenses, and when the focal lengths of said first lens unit and said rear
lens sub-unit are f1 and f13, respectively, and the Abbe number of said at
least one negative lens is .DELTA..nu.13n and the average of the Abbe
numbers of said at least three positive lenses is .DELTA..nu.13p, said
rear lens sub-unit satisfies the following conditions:
1.5.ltoreq.f13/f1.ltoreq.2.0
40<.DELTA..nu.13p-.DELTA..nu.13n.
6. The zoom lens of claim 1, characterized in that said rear lens sub-unit
has an aspherical surface AS2 provided on at least one surface thereof,
and said aspherical surface AS2, when provided on a positive refracting
surface, forms a shape in which positive refractive power becomes weaker
toward the peripheral portion of the lens, and when provided on a negative
refracting surface, forms a shape in which negative refractive power
becomes stronger toward the peripheral portion of the lens.
7. The zoom lens of claim 6, characterized in that when the aspherical
amounts at 100%, 90% and 70% of the effective diameter of the lens on
which said aspherical surface AS2 is provided are .DELTA.10, .DELTA.9 and
.DELTA.7, respectively, the following conditions are satisfied:
##EQU5##
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a zoom lens, and particularly to a zoom lens
suitable for a television camera, a phototaking camera, a video camera,
etc. which appropriately uses an aspherical surface in a portion of a lens
system, which has a large aperture in which the F number at the wide angle
end is of the order of 1.7 and moreover has a wide angle (wide angle end
angle of view 2.omega.=58.degree. to 70.degree.) and good optical
performance over the entire variable power range of as high a variable
power ratio as a variable power ratio of the order of 8.5 to 10.
2. Related Background Art
Zoom lenses having a large aperture, high variable power and high optical
performance have heretofore been required for television cameras,
phototaking cameras, video cameras, etc.
In addition, particularly in color television cameras for broadcasting,
great importance has been attached to operability and mobility and in
compliance with such requirements, compact CCD's (solid state image pickup
devices) of 2/3 inch and 1/2 inch have become the mainstream among image
pickup devices.
These CCD's have substantially uniform resolving power over the entire
image pickup range and therefore, it has been required of zoom lenses
using these that resolving power be substantially uniform from the center
of the image field to the periphery of the image field.
For example, it is desired that various aberrations such as astigmatism,
distortion and chromatic difference of magnification be corrected and the
entire image field has high optical performance. It is further desired
that the zoom lenses have a large aperture, a wide angle and a high
variable power ratio and moreover be compact and light in weight and have
a long back focus for disposing a color resolving optical system and
various filters in front of image pickup means.
Among zoom lenses, so-called four-unit zoom lenses comprising, in
succession from the object side, a first lens unit of positive refractive
power for focusing, a second lens unit of negative refractive power for
focal length change, a third lens unit of positive or negative refractive
power for correcting the movement of an image plane fluctuating with a
focal length change, and a fourth lens unit of positive refractive power
performing chiefly the imaging action are often used as zoom lenses for
color television cameras for broadcasting stations.
Among the zoom lenses of such four-unit construction, a four-unit zoom lens
having F number of the order of 1.7, a wide angle end angle of view
2.omega.=86.degree., a great aperture ratio and high variable power of a
variable power ratio of the order of 8 is proposed, for example, in
Japanese Laid-Open Patent Application No. 6-242378.
In a zoom lens, to obtain a great aperture ratio (F number 1.7 to 1.8), a
high variable power ratio (variable power ratio 8.5 to 10), a super-wide
angle (wide angle end angle of view 2.omega.=90.degree. to 96.degree.) and
moreover high optical performance over the entire variable power range, it
is necessary to appropriately set the refractive power and lens
construction of each lens unit.
Generally, to obtain a small aberration fluctuation and high optical
performance over the entire variable power range, it becomes necessary,
for example, to increase the number of lenses in each lens unit and
increase the degree of freedom of design in aberration correction.
If for this purpose, an attempt is made to achieve a zoom lens of a great
aperture ratio, a super-wide angle and a high variable power ratio, the
number of lenses will unavoidably be increased, and this leads to the
arising of the problem that the entire lens system becomes bulky, and it
becomes impossible to comply with the desire for compactness and lighter
weight.
Also, in the imaging performance, first speaking regarding the super-wide
angle of a zoom lens, distortion poses the greatest problem. This is
because distortion influences by the cube of the angle of view in the area
of the third-order aberration coefficient.
As shown in FIG. 29 of the accompanying drawings, distortion is
considerably greater under (minus) at the wide angle end (focal length
fw). From the wide angle end fw toward the telephoto end (focal length
ft), distortion becomes gradually greater in the direction of over (plus)
and passes a zoom position at which distortion is 0, and the value of over
tends to become greatest near the zoom position fm=fw.times.Z.sup.1/4.
From the focal length fm to the telephoto end ft, the over amount becomes
gradually smaller. In the foregoing, fw is the focal length at the wide
angle end, and Z is a zoom ratio.
This tendency comes to remarkably present itself as the angle of view at
the wide angle end becomes greater. In such a super-wide angle zoom lens
wherein the wide angle end angle of view 2.omega. exceeds 90.degree.,
distortion of under on the wide angle side is created and the correction
of this distortion becomes very difficult.
Next, the changing of a point at which the image contrast of the center of
the image field is best, i.e., the so-called best imaging plane, resulting
from a focal length change, poses a problem. This is attributable chiefly
to the changing of spherical aberration resulting from a focal length
change. This spherical aberration influences by the cube of the aperture
in the area of the third-order aberration coefficient and therefore, it is
the greatest problem in providing a large aperture.
Generally, the changing of spherical aberration resulting from a focal
length change tends to be under (minus) with respect to the Gaussian
imaging plane from the wide angle end at which spherical aberration is 0
to the vicinity of the zoom position fm=fw.times.Z.sup.1/4 as shown in
FIG. 30 of the accompanying drawings when the zoom ratio is Z and the
focal length at the wide angle end is fw. When the vicinity of the zoom
position fm=fw.times.Z.sup.1/4 is passed, the under amount becomes
smaller and becomes 0 at a certain zoom position, and now tends to become
over (plus).
It becomes most over (plus) near a zoom position fd=(Fno.w/Fno.t).times.ft
at which F drop in which F number becomes great (the lens system becomes
dark) begins, and when this zoom position is passed, the over amount
becomes smaller to the telephoto end and becomes substantially 0 at the
telephoto end.
In the foregoing, Fno.w and Fno.t are F numbers at the wide angle end and
the telephoto end, respectively, and ft is the focal length at the
telephoto end.
As described above, particularly in a zoom lens having a position at which
F drop begins, the correction of spherical aberration on the telephoto
side becomes very difficult.
In order to correct such changing of various aberrations effectively over
the entire variable power range, the number of lenses in the focusing lens
unit and the lens unit of the focal length changing system has heretofore
been increased. Such a technique, however, gives rise to a new problem
that the entire lens system becomes bulky and complicated.
Also, the introduction of an aspherical surface for the solution of such a
problem is done in an embodiment disclosed in the above-mentioned Japanese
Laid-Open Patent Application No. 6-242378.
However, the specification of zoom lenses has been improved, and in a zoom
lens of a great aperture ratio and moreover, a high variable power ratio
beginning from a super-wide angle, the reconsideration of the method of
introducing the aspherical surface has become necessary.
In a zoom lens of a great aperture ratio and moreover a high variable power
ratio beginning from a super-wide angle, distortion changes greatly on the
wide angle side and spherical aberration changes greatly on the telephoto
side. It has become difficult to correct these two aberrations efficiently
and well simply by introducing an aspherical surface into one of the
surfaces of a focal length changing portion.
SUMMARY OF THE INVENTION
The present invention has as its first object the provision of a so-called
four-unit zoom lens in which the refractive power of each lens unit is
appropriately set and at least one lens surface in a fore lens unit is
made into an aspherical surface to thereby reduce the changing of various
aberrations resulting from a focal length change and particularly
distortion on the wide angle side and spherical aberration on the
telephoto side is effectively corrected. The present invention has as its
second object the provision of a zoom lens which has high optical
performance over the entire variable power range and in which F number at
the wide angle end is of the order of 1.8 and which has a super-wide angle
(for example, the angle of view at the wide angle end is of the order of
2.omega.=90.degree. to 96.degree.) and a great aperture ratio and a high
variable power ratio of a variable power ratio of the order of 8.5 to 10.
The zoom lens of the present invention is:
(1) A zoom lens having, in succession from the object side, a first lens
unit of positive refractive power, a second lens unit of negative
refractive power for focal length change, a third lens unit for correcting
the changing of an imaging plane resulting from a focal length change, and
a fixed fourth lens unit of positive refractive power, wherein the first
lens unit has a front lens sub-unit of negative refractive power fixed
during focusing, an intermediate lens sub-unit movable along the optical
axis thereof for focusing, and a rear lens sub-unit of positive refractive
power fixed during focusing, and when the variable power ratio of the zoom
lens is Z and the maximum incidence height of the on-axis light beam in
the first lens unit is ht and the maximum incidence height of the off-axis
light beam of a maximum angle of view at the wide angle end in the first
lens unit is hw and the maximum incidence height of the off-axis light
beam of the maximum angle of view at a zoom position at a variable power
ratio Z.sup.1/4 is hz, an aspherical surface S1 is provided on at least
one lens surface at a position satisfying 1.65<hw/ht and 1.15<hw/hz;
(2) Particularly, the aspherical surface AS1, when provided on a positive
refracting surface, forms a shape in which positive refractive power
becomes stronger toward the peripheral portion of the lens, and when
provided on a negative refracting surface, forms a shape in which negative
refractive power becomes weaker toward the peripheral portion of the lens,
and when the combined focal length of the first lens unit in a state in
which it is in focus on an object at infinity is f1 and the aspherical
amounts (the amounts of displacement from a reference spherical surface)
in 100%, 90% and 70% of the effective diameter of the lens on which the
aspherical surface AS1 is provided are .DELTA.10, .DELTA.9 and .DELTA.7,
respectively, the aspherical surface AS1 is of a shape satisfying the
following conditions:
##EQU1##
(3) Also, the front lens sub-unit comprises, in succession from the object
side, at least two negative lenses and at least one positive lens, and the
negative lens most adjacent to the object side forms a meniscus shape
having its sharp concave surface facing the image plane side, and when the
average of the Abbe numbers of the at least two negative lenses is
.DELTA..nu.11n and the Abbe number of the positive lens is .DELTA..nu.11p,
the front lens sub-unit satisfies the following condition:
19<.DELTA..nu.11n-.DELTA..nu.11p (2)
(4) Also, the intermediate lens sub-unit as a focusing lens comprises at
least one positive lens movable toward the image plane side during
focusing on an object at infinity to an object at a close distance, and
having a shape having its sharp convex surface facing the image plane
side;
(5) Also, the rear lens sub-unit is comprised of at least one negative lens
and at least three positive lenses, and when the focal lengths of the
first lens unit and the rear lens sub-unit are f1 and f13, respectively,
and the Abbe number of the negative lens is .DELTA..nu.13n and the average
of the Abbe numbers of the at least three positive lenses is
.DELTA..nu.13p, the rear lens sub-unit satisfies the following conditions:
1.5.ltoreq.f13/f1.ltoreq.2.0 (3)
40<.DELTA..nu.13p-.DELTA..nu.13n (4)
(6) Also, the rear lens sub-unit has an aspherical surface AS2 provided on
at least one surface thereof, the aspherical surface AS2, when provided on
a positive refracting surface, forms a shape in which positive refractive
power becomes weaker toward the peripheral portion of the lens, and when
provided on a negative refracting surface, forms a shape in which negative
refractive power becomes stronger toward the peripheral portion of the
lens;
(7) Further, when in the lens of the zoom lens of item (6), the aspherical
amounts in 100%, 90% and 70% of the effective diameter of the lens on
which the aspherical surface AS2 is provided are .DELTA.10, .DELTA.9 and
.DELTA.7, respectively, the lens is of a shape satisfying the following
conditions:
##EQU2##
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a lens cross-sectional view of the wide angle end of Numerical
Value Embodiment 1 of the present invention.
FIG. 2 is a lens cross-sectional view of the wide angle end of Numerical
Value Embodiment 2 of the present invention.
FIG. 3 is a lens cross-sectional view of the wide angle end of Numerical
Value Embodiment 3 of the present invention.
FIG. 4 is a lens cross-sectional view of the wide angle end of Numerical
Value Embodiment 4 of the present invention.
FIGS. 5A, 5B and 5C show the aberrations of Embodiment 1 of the present
invention at a focal length f=5.50.
FIGS. 6A, 6B and 6C show the aberrations of Embodiment 1 of the present
invention at a focal length f=9.39.
FIGS. 7A, 7B and 7C show the aberrations of Embodiment 1 of the present
invention at a focal length f=13.75.
FIGS. 8A, 8B and 8C show the aberrations of Embodiment 1 of the present
invention at a focal length f=42.08.
FIGS. 9A, 9B and 9C show the aberrations of Embodiment 1 of the present
invention at a focal length f=46.75.
FIGS. 10A, 10B and 10C show the aberrations of Embodiment 2 of the present
invention at a focal length f=5.50.
FIGS. 11A, 11B and 11C show the aberrations of Embodiment 2 of the present
invention at a focal length f=9.39.
FIGS. 12A, 12B and 12C show the aberrations of Embodiment 2 of the present
invention at a focal length f=13.75.
FIGS. 13A, 13B and 13C show the aberrations of Embodiment 2 of the present
invention at a focal length f=42.08.
FIGS. 14A, 14B and 14C show the aberrations of Embodiment 2 of the present
invention at a focal length f=46.75.
FIGS. 15A, 15B and 15C show the aberrations of Embodiment 3 of the present
invention at a focal length f=5.20.
FIGS. 16A, 16B and 16C show the aberrations of Embodiment 3 of the present
invention at a focal length f=9.01.
FIGS. 17A, 17B and 17C show the aberrations of Embodiment 3 of the present
invention at a focal length f=13.00.
FIGS. 18A, 18B and 18C show the aberrations of Embodiment 3 of the present
invention at a focal length f=40.11.
FIGS. 19A, 19B and 19C show the aberrations of Embodiment 3 of the present
invention at a focal length f=46.80.
FIGS. 20A, 20B and 20C show the aberrations of Embodiment 4 of the present
invention at a focal length f=5.00.
FIGS. 21A, 21B and 21C show the aberrations of Embodiment 4 of the present
invention at a focal length f=8.89.
FIGS. 22A, 22B and 22C show the aberrations of Embodiment 4 of the present
invention at a focal length f=12.50.
FIGS. 23A, 23B and 23C show the aberrations of Embodiment 4 of the present
invention at a focal length f=37.50.
FIGS. 24A, 24B and 24C show the aberrations of Embodiment 4 of the present
invention at a focal length f=50.00.
FIG. 25 shows the optical path of a portion of FIG. 1.
FIG. 26 shows the optical path of a portion of FIG. 1.
FIG. 27 shows the optical path of a portion of FIG. 1.
FIG. 28 shows the optical path of a portion of FIG. 1.
FIG. 29 is an illustration of the changing of an aberration resulting from
the focal length change of a zoom lens.
FIG. 30 is an illustration of the changing of an aberration resulting from
the focal length change of a zoom lens.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 to 4 are lens cross-sectional views of Numerical Value Embodiments
1 to 4 of the present invention at the wide angle end.
In FIGS. 1 to 4, the letter F designates a focusing lens unit (fore lens
unit) of positive refractive power as a first lens unit having a fixed
front lens sub-unit F1 of negative refractive power having at least two
negative lenses and at least one positive lens, an intermediate lens
sub-unit F2 movable on the optical axis thereof during focusing, and a
fixed rear lens sub-unit F3 of positive refractive power.
The letter V denotes a variator for focal length change having negative
refractive power as a second lens unit, and the variator V is monotonously
moved on the optical axis toward the imaging plane to thereby effect focal
length change from the wide angle end (wide) to the telephoto (tele) end.
The letter C designates a compensator of negative refractive power as a
third lens unit having a convex locus toward the object side on the
optical axis to correct the changing of the imaging plane resulting from a
focal length change and moved non-linearly. The variator V and the
compensator C together constitute a focal length changing system (zooming
system).
The letters SP denotes a stop which determines open f number, and the
letter R designates a fixed relay lens unit of positive refractive power
as a fourth lens unit. The letter P denotes a color resolving prism, an
optical filter or the like, and in FIGS. 1 to 4, it is shown as a glass
block.
The present embodiment is a super-wide angle zoom lens which has a zoom
ratio Z of 8.5 times or greater and in which the wide angle end angle of
view 2a exceeds 90.degree., and further, in order to realize a zoom lens
which has been made large in aperture in the entire zoom area, it is
suitable as a zoom lens of a wide angle system which will satisfy a
condition expression that fw/IS<0.53, where fw and IS are the focal length
of the entire system at the wide angle end and the size of the
photo-taking image field (the diagonal length of the image field),
respectively.
Description will now be made of the features of the aspherical surface of
the zoom lens according to the present invention.
In a zoom lens wherein the wide angle end angle of view 2a begins from
2.omega.=90.degree. to 96.degree. and the zoom ratio is on the order of
8.5 to 10 times, the incidence heights of an on-axis ray of light onto the
fore lens unit and the variator become successively higher from the wide
angle end to the telephoto end, as shown in FIGS. 25 to 28, and in a zoom
lens having F drop, the incidence heights become highest at an F drop
starting position (zoom position fd in FIG. 27). At the telephoto end, due
to the F drop, the incidence heights become constant in the fore lens
unit, and become low in the variator.
In contrast, a ray of light of the incidence height of the maximum off-axis
ray of light (the height of a light beam of the maximum off-axis light
beams which is farthest from the optical axis) passes through particularly
the front lens sub-unit of the fore lens unit over the effective diameter
thereof at the wide angle end, but the ray of light of this incidence
height in the front lens sub-unit suddenly becomes low at a zoom position
fm=fw.times.Z.sup.1/4. On the other hand, conversely, the incidence height
in the rear lens sub-unit of the fore lens unit suddenly becomes high.
This tendency becomes more remarkable when an attempt is made to achieve a
wider angle, a higher magnification, and compactness and lighter weight.
To efficiently correct distortion which changes greatly on the wide angle
side when an aspherical surface is provided in the fore lens unit to
thereby suppress the changing of aberrations, it is necessary to dispose
the aspherical surface at an appropriate position.
So, in the present embodiment, the greatest feature is that in order to
correct distortion which influences by the cube of the angle of view,
within the entire variable power range, an aspherical surface AS1 is
provided on at least one of the lens surfaces constituting the fore lens
group which satisfies 1.65<hw/ht and 1.15<hw/hz, where ht is the maximum
incidence height of the on-axis light beam, hw is the incidence height of
the off-axis light beam at the maximum angle of view at the wide angle
end, and hz in the incidence height of the off-axis light beam of the
maximum angle of view at a zoom position at a variable power ratio
Z.sup.1/4.
Also, this aspherical surface is of a shape in which when an aspherical
surface for correcting the changing of distortion on the wide angle side
is provided on a positive refracting surface in the fore lens unit,
positive refractive power becomes stronger toward the peripheral portion
of the lens. On the other hand, when the aspherical surface is provided on
a negative refracting surface, the aspherical surface is made into a shape
in which negative refractive power becomes weaker toward the peripheral
portion of the lens, whereby it is corrected so that the distortion near
the wide angle end becomes under (minus).
Now, such shape of the aspherical surface corrects under distortion well
near the wide angle end, but conversely speaking, regarding the distortion
at a zoom position at a variable power ratio Z.sup.1/4 this produces a
contrary result, and over (plus) distortion attributable to the strong
positive refractive power in the fore lens unit at the zoom position at
the variable power ratio Z.sup.1/4 is increased more strongly by the
aspherical surface effect, whereby it becomes difficult to suppress the
distortion.
So, the satisfaction of the above-mentioned condition that 1.65<hw/ht shows
that the off-axis ray of light passes only near the wide angle end in the
entire variable power range and the difference from the incidence height
of the on-axis ray of light on the telephoto side is great, whereby the
influence upon the changing or the like of spherical aberration on the
telephoto side is suppressed to the utmost while the distortion at the
wide angle end by a wider angle is corrected well. In addition, the
concurrent satisfaction of the above-mentioned condition that 1.15<hw/hz
shows that the off-axis ray of light passes only near the wide angle end
in the entire variable power range and the difference from the incidence
height of the off-axis light beam of a maximum angle of view near the zoom
position at the variable power ratio Z.sup.1/4 is great, and it is
avoided that the over (plus) distortion attributable to the strong
positive refractive power in the fore lens unit at the zoom position at
the variable power ratio Z.sup.1/4 is increased more strongly by the
aspherical surface effect. Thereby, the influence upon the changing or the
like of the distortion on the telephoto side is suppressed while the
distortion at the wide angle end by a wider angle is corrected well.
More desirably, in accordance with an embodiment which will be described
later, the position of the aspherical surface is applied to a location of
1.80<hw/ht and 1.20<hw/hz, whereby it becomes possible to provide a more
desirable aspherical surface effect.
Further, in the present embodiment, in order to effectively correct the
distortion at the wide angle end by the wider angle, the aspherical amount
of the aspherical surface shape of the fore lens unit is set so as to
satisfy the aforementioned conditional expression (1). What this condition
means is that the central portion (the vicinity of the optical axis) of
the aspherical lens is substantially spherical (or flat) and the
aspherical amount (the amount of displacement from a reference spherical
surface) becomes considerably greater toward the periphery of the lens.
The above-mentioned conditional expression (1) prescribes the shape of
this aspherical surface, and provides such action that the distortion
correcting effect of the aspherical surface is displayed only in some zoom
range of the entire zoom area near the wide angle end in which negative
distortion is liable to occur, and in the other zoom area, the influence
upon spherical aberration, astigmatism, coma, etc. is made as small as
possible.
Next, in order to effectively correct optical performance for distortion
and particularly chromatic aberration regarding the fore lens unit, the
front lens sub-unit F1 in the present embodiment is comprised, in
succession from the object side, of at least two negative lenses and at
least one positive lens, and the negative lens most adjacent to the object
side is made into a meniscus shape having a sharp concave surface facing
the imaging plane side, whereby the occurrence of distortion at the wide
angle end is suppressed to the utmost. Further, the achromatizing
conditional expression (2) in the front lens sub-unit is satisfied to
thereby effectively correct particularly the achromatism of the off-axis
ray of light on the wide angle side.
If the lower limit value of conditional expression (2) is exceeded,
achromatism will become insufficient and particularly the changing of
chromatic difference of magnification on the wide angle side will greatly
remain.
Now, the intermediate lens sub-unit F2 in the present embodiment introduces
thereinto the so-called inner focus system for moving it toward the
imaging plane side when effecting the focusing on an object at infinity to
an object at a very close distance.
By doing so, the changing of aberrations by the object distance is
corrected effectively and at the same time, the effects of downsizing the
entire zoom lens and mitigating the focus operating torque are achieved.
Also, the intermediate lens sub-unit F2 comprises at least one positive
lens and the shape thereof is made into a shape having a sharp convex
surface facing the imaging plane side to thereby achieve the effect of
correcting distortion greatly changing to under (minus) at the wide angle
end.
On the other hand, the rear lens sub-unit F3 is comprised of at least one
negative lens and at least three positive lenses, and the focal length of
the rear lens sub-unit F3 relative to the entire fore lens group is set as
defined in conditional expression (3).
If the lower limit value of conditional expression (3) is exceeded, the
radii of curvature of the lenses constituting the rear lens sub-unit F3
tend to suddenly become smaller, and the changing of aberrations
particularly on the telephoto side will become great. The number of
constituent lenses as the degree of freedom of design for correcting this
needs to be great and it becomes difficult to achieve a larger aperture
and downsizing. If the upper limit value of conditional expression (3) is
exceeded, positive Petzval sum will remarkably decrease and it will become
difficult to correct negative Petzval sum occurring in the variator V.
Also, the principal point of the imaging plane as the entire fore lens
unit comes in and this produces a contrary result against downsizing.
Further, the achromatizing conditional expression (4) in the rear lens
sub-unit F3 is satisfied, and the achromatism of the on-axis ray of light
particularly on the telephoto side is corrected.
If the lower limit value of conditional expression (4) is exceeded,
achromatism will become insufficient and the on-axis chromatic aberration
on the telephoto side will remain.
In the zoom lenses shown in FIGS. 1 to 4, the above-described conditions
are satisfied, whereby the changing of aberrations is effectively
corrected over the entire variable power range and high optical
performance is obtained.
Now, in Numerical Value Embodiments 2 and 4 in the present embodiment, an
aspherical surface for correcting the changing of spherical aberration on
the telephoto side which remains to some extent is provided on at least
one surface in the rear lens sub-unit F3 of the fore lens unit F.
Particularly, when the aspherical surface for correcting the changing of
spherical aberration on the telephoto side is provided on the positive
refracting surface of the rear lens sub-unit in the fore lens unit, the
lens is made into a shape in which positive refractive power becomes
weaker toward the peripheral portion of the lens, and when the aspherical
surface is provided on the negative refracting surface of the rear lens
sub-unit, the lens is made into a shape in which negative refractive power
becomes stronger toward the peripheral portion of the lens, whereby it is
corrected that the spherical aberration at the telephoto end becomes under
(minus).
Further, in Embodiments 2 and 4, a spherical shape of such a shape that
satisfies the aforementioned conditional expression (5) is adopted to
effectively correct the spherical aberration at the telephoto end by the
higher variable power of zoom. What this conditional expression means is a
shape in which the center of the optical axis of the aspherical surface is
substantially approximate to the spherical shape of the reference
spherical surface and the aspherical amount becomes greater toward the
periphery of the lens.
This conditional expression is for causing the spherical aberration
correcting effect of the aspherical surface to be displayed only in some
zoom range of the zoom area which is near the telephoto end in the
variable power system of a zoom lens so that in the other zoom areas, the
influence upon astigmatism, coma, etc. may not be provided as far as
possible.
As the additional effect of this aspherical surface, it becomes also
possible to suppress the over (plus) distortion attributable to the fact
that the off-axis incidence height in the rear lens sub-unit at a zoom
position fm=fw.times.Z.sup.1/4 suddenly becomes high, whereby the
off-axis ray of light is strongly jumped up by the positive refractive
power of the fore lens unit. That is, it is very effective to provide the
aspherical surface on that lens surface adjacent to the object side of the
fore lens unit in which the on-axis ray incidence height on the telephoto
side is high and the change in the off-axis ray incidence height on the
wide angle side is great.
Also, in Embodiments 2 and 4, in the variator V, concave, convex, concave,
convex and concave lenses are disposed in succession from the object side.
The negative lens most adjacent to the object side is made into a meniscus
shape having its sharp concave surface facing the imaging plane, whereby
the distortion at the wide angle end is effectively corrected.
The changing of chromatic aberration and particularly chromatic difference
of magnification itself are corrected by the combination of the second and
third concave and convex lenses. The variator V is comprised of five
lenses and the thickness of the entire variator V is increased and
therefore, if the correcting surface for achromatism as the variator is
present closer to the imaging plane side, the deviation of the position of
the principal point by the wavelength of the variator becomes greater and
chromatic difference of magnification occurs greatly. Therefore, as in the
construction of the embodiment, the cardinal point of achromatism as the
variator V is made to exist on the object side to thereby correct
chromatic difference of magnification well.
Further, the combination of the fourth and fifth concave and convex lenses
is used and an appropriate refractive index is set between the two,
thereby correcting the coma on the telephoto side in particular. The
positive lens and the negative lens adopt one of the forms of joint and
separation when the influences of high-order aberrations are taken into
consideration, and an appropriate refractive index difference for
sufficiently displaying the diverging effect of coma particularly when the
form of joint is adopted is set.
As described above, in the present embodiment, the lens surface on which
the aspherical surface is provided is appropriately set to thereby
effectively correct the changing of the distortion on the wide angle side
and the spherical aberration on the telephoto side, thus obtaining high
optical performance over the entire variable power range.
The features of each embodiment (numerical value embodiment) of the present
invention will now be described.
Embodiment 1 shown in FIG. 1 has a zoom ratio of 8.5 times and the wide
angle end angle of view 2.omega. exceeds 90.degree.. R1 to R15 designate a
fore lens unit F. R1 to R6 denote F1 fixed during focusing and having
negative power (refractive power). R7 to R8 designate a lens unit F2
having the focusing action and movable toward the imaging plane side
during the focusing on an object at infinity to an object at a very close
distance, and R9 to R15 denote F3 fixed during focusing and having
positive power. R16 to R23 designate a variator V monotonously movable
toward the imaging plane side from wide (wide angle end) to tele
(telephoto end) for focal length change. R24 to R26 denote a compensator C
having the image point correcting action resulting from focal length
change, and having negative power and movable toward the object side so as
to describe a convex area during the focal length change from wide to
tele. SP(27) designates a stop. R28 to R44 denote a relay lens unit R
having the imaging action, and R45 to R47 designate a glass block
equivalent to a color resolving prism.
In this Embodiment 1, when as an index for wider angles, the ratio between
the wide angle end focal length fw of the entire zoom lens system and the
photo-taking image field IS is defined as fw/IS, the zoom lens has a
super-wide angle of fw/IS=0.5. For these wider angles, in the fore lens
unit, the off-axis ray incidence height becomes great on the wide angle
side and therefore, F1 which greatly influences various aberrations is
comprised, in succession from the object side, of three concave, concave
and convex lenses, and the concave lens most adjacent to the object side
is made into a meniscus shape having its sharp concave surface facing the
imaging plane side, whereby the occurrence of distortion in the fore lens
unit is suppressed.
Also, a so-called inner focusing system using F2 as a focusing movable lens
unit is adopted as a focusing system, whereby the changing of aberrations
due to the object distance is corrected effectively and at the same time,
effects such as the downsizing of the entire zoom lens and the mitigation
of focus operating torque are achieved.
Further, the on-axis ray incidence height becomes great on the telephoto
side and therefore, F3 which greatly influences the various aberrations on
the telephoto side is comprised, in succession from the object side, of
four lenses which are concave, convex, convex and convex lenses, and
spherical aberration is caused to diverge by the concave lens and the
occurrence of spherical aberration in the fore lens group suppressed.
The aforementioned conditional expressions are
.DELTA..nu.11n-.DELTA..nu.11p=20.07, f13/f1=1.636 and
.DELTA..nu.13p-.DELTA..nu.13n=41.83.
The variator V is comprised of four lenses which are concave, concave,
convex and concave lenses, and spherical aberration, coma, etc. are caused
to diverge by the convex lens to thereby suppress the occurrence of
various aberrations in the variator.
The compensator is comprised of two concave and convex lenses, and
spherical aberration and chromatic aberration are caused to diverge by the
boundary surface therebetween to thereby suppress the occurrence of
various aberrations.
The aspherical surface is provided on a surface R1, and the aspherical
surface on the surface R1 effectively utilizes that the off-axis ray of
light passes only near the wide angle end in the entire variable power
range and the difference from the incidence height of the on-axis ray of
light on the telephoto side is great and that the difference from the
incidence height of the off-axis light beam of a maximum angle of view
near the zoom position at the variable power ratio Z.sup.1/4 is great,
and hw/ht=2.886 and hw/hz=1.306.
The direction of the aspherical surface is a direction in which positive
power becomes stronger as the amount of separation from the optical axis
becomes greater, and in order to efficiently correct distortion and
spherical aberration up to high-order areas, up to aspherical surface
coefficients B, C, D and E are used. The aspherical amount at this time is
1057.9 .mu.m at the maximum height of the incident ray of light on R1.
FIGS. 5A to 5C, FIGS. 6A to 6C, FIGS. 7A to 7C, FIGS. 8A to 8C, FIGS. 9A to
9C, FIGS. 10A to 10C, FIGS. 11A to 11C, FIGS. 12A to 12C, FIGS. 13A to
13C, FIGS. 14A to 14C, FIGS. 15A to 15C, FIGS. 16A to 16C, FIGS. 17A to
17C, FIGS. 18A to 18C, FIGS. 19A to 19C, FIGS. 20A to 20C, FIGS. 21A to
21C, FIGS. 22A to 22C, FIGS. 23A to 23C and FIGS. 24A to 24C show
spherical aberration, astigmatism and distortion at respective zoom
positions.
Embodiment 2 shown in FIG. 2 has a zoom ratio of 8.5 times and the wide
angle end angle of view 2.omega. exceeds 90.degree.. Moreover, it is a
zoom lens entirely free of F drop on the telephoto side. R1 to R17
designate a fore lens unit F. R1 to R8 denotes F1 fixed during focusing
and having negative power (refractive power), R9 to R10 designate F2
having the focusing action and movable toward the imaging plane side
during the focusing on an object at infinity to an object at a very close
distance, and R11 to R17 denote F3 fixed during focusing and having
positive power. R18 to R26 designate a variator V monotonously movable
from wide (wide angle end) to tele (telephoto end) for focal length
change. R27 to R29 denote a compensator C having the image point
correcting action resulting from focal length change and having negative
power, and movable toward the object side so as to describe a convex area
during the focal length change from wide to tele. SP(30) designates a
stop. R31 to R47 denote a relay lens unit R having the imaging action, and
R48 to R50 designate a glass block equivalent to a color resolving prism.
In this Embodiment 2, when as an index for wider angles, the ratio between
the wide angle end focal length fw of the entire zoom lens system and the
photo-taking image field IS is defined as fw/IS, the zoom lens has a
super-wide angle of fw/IS=0.5. In addition, in this Embodiment 2, F drop
on the telephoto side does not occur at all. For these wider angles and
large apertures, in the fore lens unit, the off-axis incidence height
becomes great on the wide angle side and therefore, F1 which greatly
influences the various aberrations on the wide angle side is comprised, in
succession from the object side, of four lenses which are concave,
concave, concave and convex lenses, and the concave lens most adjacent to
the object side is made into a meniscus shape having its sharp concave
surface facing the imaging plane side to thereby suppress the occurrence
of distortion in the fore lens unit.
Also, a so-called inner focusing system using F2 as a focusing movable lens
unit is adopted as a focusing system, whereby the changing of aberrations
due to the object distance is corrected effectively and at the same time,
effects such as the downsizing of the entire zoom lens and the mitigation
of focus operating torque are achieved.
Further, the on-axis ray incidence height becomes great on the telephoto
side and therefore, F3 which greatly influences the various aberrations on
the telephoto side is comprised, in succession from the object side, of
four lenses which are concave, convex, convex and convex lenses, and
spherical aberration is caused to diverge by the concave lens and the
occurrence of spherical aberration in the fore lens unit is suppressed.
The aforementioned conditional expressions are
.DELTA..nu.11n-.DELTA..nu.11p=28.12, f13/f1=1.67 and
.DELTA..nu.13p-.DELTA..nu.13n=41.83.
The variator V is comprised of five lenses which are concave, convex,
concave, convex and concave lenses, and the second convex lens and the
third concave lens are provided with an appropriate Abbe number difference
therebetween to thereby effect achromatism as much as possible on the
object side, and the fourth convex lens and the fifth concave lens are
provided with an appropriate refractive index difference therebetween to
thereby cause spherical aberration, coma etc. to diverge, thus suppressing
the occurrence of various aberrations in the variator.
The compensator C is comprised of two lenses which are concave and convex
lenses, and spherical aberration and chromatic aberration are caused to
diverge by the boundary surface therebetween, thereby suppressing the
occurrence of various aberrations.
Aspherical surfaces are provided on a surface R3 and a surface R16, and the
aspherical surface on the surface R3 effectively utilizes that the
off-axis ray of light passes only near the wide angle end in the entire
variable power range and the difference from the on-axis ray of light on
the telephoto side is great and that the off-axis ray of light passes only
near the wide angle end in the entire variable power range and the
difference from the incidence height of the off-axis light beam of a
maximum angle of view near the zoom position at a variable power ratio
Z.sup.1/4 is great, and hw/ht=1.763 and hw/hz=1.162.
The direction of the aspherical surfaces is a direction in which positive
power becomes stronger as the amount of separation from the optical axis
becomes greater, and in order to efficiently correct distortion and
spherical aberration up to high-order areas, up to aspherical surface
coefficients B, C, D and E are used. The aspherical amount at this time is
336.3 .mu.m at the maximum height of the incident ray onto R1.
The aspherical surface provided on the surface R16 corrects the spherical
aberration occurring greatly on the telephoto side because appropriate F
drop is not set. The direction of the aspherical surface is a direction in
which positive power becomes weaker as the amount of separation from the
optical axis becomes greater, and in order to efficiently correct
distortion and spherical aberration up to high-order areas, up to
aspherical surface coefficients B, C, D and E are used. The aspherical
amount at this time is 198.1 .mu.m at the maximum height of the incident
ray onto R16. At the same time, this aspherical shape is a direction in
which the over distortion at the variable power ratio Z.sup.1/4 is
mitigated, and is provided on R16 because the more effective is a lens
surface on which the incidence height of the on-axis ray is great on the
telephoto side and on which the incidence height of the off-axis ray at
the variable power ratio Z.sup.1/4 is great.
FIGS. 10A to 10C to 14A to 14C show spherical aberration, astigmatism and
distortion at respective zoom positions.
Embodiment 3 shown in FIG. 3 has a zoom ratio of nine times, and the wide
angle end angle of view 2.omega. exceeds 93.degree..
R1 to R17 designate a fore lens unit F. R1 to R8 denote F1 fixed during
focusing and having negative power (refractive power), R9 to R10 designate
F2 having the focusing action and movable to the imaging plane side during
the focusing on an object at infinity to an object at a very close
distance, and R11 to R17 denote F3 fixed during focusing and having
positive power. R18 to R25 designate a variator V monotonously movable
toward the imaging plane side from wide (wide angle end) to tele
(telephoto end) for focal length change. R26 to R28 denote a compensator C
having the image point correcting action resulting from a focal length
change and having negative power, and movable toward the object side so as
to describe a convex area during the focal length change from wide to
tele. SP(29) designates a stop. R30 to R46 denote a relay lens unit R
having the imaging action, and R47 to R49 designate a glass block
equivalent to a color resolving prism.
In this Embodiment 3, when as an index for wider angles, the ratio between
the wide angle end focal length fw of the entire zoom lens system and the
photo-taking image field IS is defined as fw/IS, the zoom lens has a
super-wide angle of tw/IS=0.473. For these wider angles, in the fore lens
unit, the off-axis ray incidence height becomes great on the wide angle
side and therefore, F1 which greatly influences the various aberrations on
the wide angle side is comprised, in succession from the object side, of
four lenses which are concave, concave, concave and convex lenses, and the
concave lens most adjacent to the object side is made into a meniscus
shape having its sharp concave surface facing the imaging plane side to
thereby suppress the occurrence of distortion in the fore lens unit.
A so-called inner focusing system using F2 as a focusing movable lens unit
is adopted as a focusing system, whereby the changing of aberrations due
to the object distance is corrected effectively and at the same time,
effects such as the downsizing of the entire zoom lens and the mitigation
of focus operating torque are achieved.
Further, the on-axis ray incidence height becomes great on the telephoto
side and therefore, F3 which grately influences the various aberrations on
the telephoto side is comprised, in succession from the object side, of
four lenses which are concave, convex, convex and convex lenses, and
spherical aberration is caused to diverge by the concave lens and the
occurrence of spherical aberration in the fore lens unit is suppressed.
The aforementioned conditional expressions are
.DELTA..nu.11n-.DELTA..nu.11p=27.56, f13/f1=1.829 and
.DELTA..nu.13p-.DELTA..nu.13n=41.83.
The variator V is comprised of four lenses which are concave, concave,
convex and concave lenses, and spherical aberration, coma, etc. are caused
to diverge by the convex lens and the occurrence of various aberrations in
the variator is suppressed.
The compensator C is comprised of two lenses which are concave and convex
lenses, and spherical aberration and chromatic aberration are caused to
diverge by the boundary surface therebetween and the occurrence of various
aberrations is suppressed.
An aspherical surface is provided on a surface R1, and the aspherical
surface on the surface R1 effectively utilizes that the off-axis ray of
light passes only near the wide angle end in the entire variable power
range and the difference from the incidence height of the on-axis ray of
light on the telephoto side is great and that the off-axis ray of light
passes only near the wide angle end in the entire variable power range and
the difference from the incidence height of the off-axis light beam of a
maximum angle of view near the zoom position at a variable power ratio
Z.sup.1/4 is great, and hw/ht=3.358 and hw/hz=1.352.
The direction of the aspherical surface is a direction in which positive
power becomes stronger as the amount of separation from the optical axis
becomes greater, and in order to efficiently correct distortion and
spherical aberration up to high-order areas, up to aspherical surface
coefficients B, C, D and E are used. The aspherical amount at this time is
805.2 .mu.m at the maximum height of the incident ray on R1.
FIGS. 15A to 15C to FIGS. 19A to 19C show spherical aberration, astigmatism
and distortion at respective zoom positions.
Embodiment 4 shown in FIG. 4 has a zoom ratio of ten times and the wide
angle end angle of view 2.omega. exceeds 95.degree.. R1 to R17 designate a
fore lens unit F. R1 to R8 denote F1 fixed during focusing and having
negative power (refractive power), R9 to R10 designate F2 having the
focusing action and movable toward the imaging plane side during the
focusing on an object at infinity to an object at a very close distance,
and R11 to R17 denote F3 fixed during focusing and having positive power.
R18 to R26 designate a variator V monotonously movable toward the imaging
plane side from wide (wide angle end) to tele (telephot end) for focal
length change. R27 to R29 denote a compensator C having the image point
correcting action resulting from a focal length change and having negative
power, and movable toward the object side so as to describe a convex area
during the focal length change from wide to tele. SP(30) designates a
stop. R31 to R47 denote a relay lens unit having the imaging action, and
R48 to R50 designate a glass block equivalent to a color resolving prism.
In this Embodiment 4, when as an index for wider angles, the ratio between
the wide angle end focal length fw of the entire zoom lens system and the
photo-taking image field IS is defined as fw/IS, the zoom lens has a
super-wide angle of fw/IS=0.454. For these wider angles, in the fore lens
unit, the off-axis ray incidence height becomes great on the wide angle
side and therefore, F1 which greatly influences the various aberrations on
the wide angle side is comprised, in succession from the object side, of
four lenses which are concave, concave, concave and convex lenses, and the
concave lens most adjacent to the object side is made into a meniscus
shape having its sharp concave surface facing the imaging plane side to
thereby suppress the occurrence of distortion in the fore lens unit.
Also, a so-called inner focusing system using F2 as a focusing movable lens
unit is adopted as a focusing system, whereby the changing of aberrations
due to the object distance is corrected effectively and at the same time,
effects such as the downsizing of the entire zoom lens and the mitigation
of focus operating torque are achieved.
Further, the on-axis ray incidence height becomes great on the telephoto
side and therefore, F3 which greatly influences the various aberrations on
the telephoto side is comprised, in succession from the object side, of
four lenses which are concave, convex, convex and convex lenses, and
spherical aberration is caused to diverge by the concave lens and the
occurrence of spherical aberration in the fore lens unit is suppressed.
The aforementioned conditional expressions are
.DELTA..nu.11n-.DELTA..nu.11p=25.86, f13/f1=1.82 and
.DELTA..nu.13p-.DELTA..nu.13n=41.83.
The variator V is comprised of five lenses which are concave, convex,
concave, convex and concave lenses, and the second convex lens and the
third concave lens are provided with an appropriate Abbe number difference
therebetween and achromatism is effected as far as possible on the object
side, and the fourth convex lens and the fifth concave lens are provided
with an appropriate refractive index difference therebetween, whereby
spherical aberration, coma, etc. are caused to diverge to thereby suppress
the occurrence of various aberrations in the variator.
The compensator C is comprised of two lenses which are concave and convex
lenses, and spherical aberration and chromatic aberration are caused to
diverge by the boundary surface therebetween to thereby suppress the
occurrence of various aberrations.
Aspherical surfaces are provided on a surface R1 and a surface R16, and the
aspherical surface on the surface R1 effectively utilizes that the
off-axis ray of light passes only near the wide angle end in the entire
variable power range and the difference from the incidence height of the
on-axis ray of light on the telephoto side is great and that the off-axis
ray of light passes only near the wide angle end in the entire variable
power range and the difference from the incidence height of the off-axis
light beam of a maximum angle of view near the zoom position at the
variable power ratio Z.sup.1/4 is great, and hw/ht=3.561 and hw/hz=1.383.
The direction of the aspherical surface is a direction in which positive
power becomes stronger as the amount of separation from the optical axis
becomes greater, and in order to efficiently correct distortion and
spherical aberration up to high-order areas, up to aspherical surface
coefficients B, C, D and E are used. The aspherical amount at this time is
1400.6 .mu.m at the maximum height of the incident ray of light on R1.
The aspherical surface provided on the surface R16 corrects the spherical
aberration on the telephoto side. The direction of the aspherical surface
is a direction in which positive power becomes weaker as the amount of
separation from the optical axis becomes greater, and in order to
efficiently correct distortion and spherical aberration up to high-order
areas, up to aspherical surface coefficients B, C, D and E are used. The
aspherical amount at this time is 135.5 .mu.m at the maximum height of the
incident ray of light on R16. This aspherical shape, at the same time, is
in a direction in which the over distortion at the variable power ratio
Z.sup.1/4 is mitigated, and is provided on R16 because a lens surface in
which the on-axis ray incidence height is great on the telephoto side and
the off-axis ray incidence height at the variable power ratio Z.sup.1/4
is great is more effective.
FIGS. 20A to 20C, 21A to 21C, 22A to 22C, 23A to 23C and FIGS. 24A to 24C
show spherical aberration, astigmatism and distortion at respective zoom
positions.
Some numerical value embodiments of the present invention will be shown
below. In the numerical value embodiments, Ri represents the radius of
curvature of the ith lens surface from the object side, Di represents the
thickness and air space of the ith lens from the object side, and Ni and
vi represent the refractive index and Abbe number, respectively, of the
material of the ith lens from the object side.
When the X-axis is in the direction of the optical axis and the H-axis in a
direction perpendicular to the optical axis and the direction of travel of
light is positive and R is the paraxial radius of curvature and k, B, C, D
and E are aspherical surface coefficients, the aspherical shape is
represented by the following expression:
##EQU3##
__________________________________________________________________________
(Numerical Value Embodiment 1)
f = 5.5 to 46.75 fno +1.8 to 2.0 2w = 90.degree. to
__________________________________________________________________________
13.4.degree.
(aspherical
r1 = 767.772
d1 = 2.50
n1 = 1.82017
.nu.1 = 46.6
surface)
r2 = 32.686
d2 = 19.47
r3 = -78.489
d3 = 2.00
n2 = 1.82017
.nu.2 = 46.6
r4 = 136.127
d4 = 0.20
r5 = 88.252
d5 = 11.30
n3 = 1 76859
.nu.3 = 26.5
r6 = -76.340
d6 = 1.24
r7 = 1861.454
d7 = 5.38
n4 = 1.49845
.nu.4 = 81.6
r8 = -97.352
d8 = 10.10
r9 = -658.162
d9 = 2.00
n5 = 1.81265
.nu.5 = 254
r10 = 44.836
d10 = 10.21
n6 = 1.49845
.nu.6 = 81.6
r11 = -166.063
d11 = 0.20
r12 = 85.569
d12 = 10.07
n7 = 1.60520
.nu.7 = 65.6
r13 = -71.853
d13 = 0.20
r14 = 45.705
d14 = 4.79
n8 = 1.73234
.nu.8 = 54.7
r15 = 94.082
d15 = variable
r16 = 36.489
d16 = 0.80
n9 = 1.88814
.nu.9 = 40.8
r17 = 14.884
d17 = 4.67
r18 = -63.944
d18 = 0.80
n10 = 1.88814
.nu.10 = 40.8
r19 = 25.851
d19 = 2.80
r20 = 23.222
d20 = 5.03
n11 = 1.79191
.nu.11 = 25.7
r21 = -26.612
d21 = 0.84
r22 = -21.208
d22 = 0.80
n12 = 1.88814
.nu.12 = 40.8
r23 = 132.833
d23 = variable
r24 = -27.903
d24 = 0.80
n13 = 1.77621
.nu.13 = 49.6
r25 = 64.341
d25 = 2.57
n14 = 1.85501
.nu.14 = 23.9
r26 = -205.966
d26 = variable
r27 = (stop)
d27 = 1.20
r28 = -340.189
d28 = 3.94
n15 = 1.50014
.nu.15 = 65.0
r29 = -32.038
d29 = 0.15
r30 = 107.653
d30 = 3.72
n16 = 1.50349
.nu.16 = 56.4
r31 = -60.918
d31 = 0.15
r32 = 45.740
d32 = 6.78
n17 = 1.50349
.nu.17 = 56.4
r33 = -33.931
d33 = 1.20
n18 = 1.82017
.nu.18 = 46.6
r34 = -384.229
d34 = 30.00
r35 = 56.736
d35 = 5.15
n19 = 1 51825
.nu.19 = 64.2
r36 = -37.851
d36 = 0.15
r37 = -68.700
d37 = 1.20
n20 = 1.88814
.nu.20 = 40.8
r38 = 21.283
d38 = 5.78
n21 = 1.51825
.nu.21 = 64.2
r39 = -170.854
d39 = 0.15
r40 = 1021.831
d40 = 6.49
n22 = 1.55099
.nu.22 = 45.8
r41 = -17.525
d41 = 1.20
n23 = 1.81265
.nu.23 = 25.4
r42 = -60.667
d42 = 0.15
r43 = 60.452
d43 = 5.36
n24 = 1.65223
.nu.24 = 33.8
r44 = -41.692
d44 = 5.00
r45 = .infin.
d45 = 30.00
n25 = 1.60718
.nu.25 = 38.0
r46 = .infin.
d46 = 16.20
n26 = 1.51825
.nu.26 = 64.1
r47 = .infin.
__________________________________________________________________________
TABLE 1
______________________________________
Variable Focal length
spacing 5.50 9.39 13.75 42.08
46.75
______________________________________
d15 0.56 14.25 21.71 35.86
36.71
d23 42.39 26.25 17.49 5.95 6.14
d26 1.00 3.44 4.75 2.14 1.10
______________________________________
aspherical surface shape
surface R1
reference spherical
aspherical
surface R = 767.772
amount (R1)
h .DELTA.
aspherical surface
70% (23.47 mm) 300.2 .mu.m
coefficient
90% (30.18 mm) 740.4 .mu.m
k = 4.499 .times. D.sup.2
100% (33.53 mm) 1057.9 .mu.m
B = 1.628 .times. D.sup.-6
C = -4.253 .times. D.sup.-10
D = 2.066 .times. D.sup.-13
E = -1.675 .times. D.sup.-16
Zoom parameter
fw/IS = 0.5
hw/ht = 2.886
hw/hz = 1.306
.DELTA..nu.11n-.DELTA..nu.11p = 20.07
f13/f1 = 1.636
.DELTA..nu.13n-.DELTA..nu.13p = 41.83
______________________________________
__________________________________________________________________________
(Numerical Value Embodiment 2)
f = 5.5 to 46.75 fno = 1.8 2w = 90.degree. to 13.4.degree.
__________________________________________________________________________
(aspherical
r1 = 97.068
d1 = 2.50
n1 = 1.77621
.nu.1 = 49.6
surface)
r2 = 33.932
d2 = 18.98
r3 = -665.567
d3 = 2.00
n2 = 1.69979
.nu.2 = 55.5
r4 = 80.425
d4 = 9.76
r5 = -136.818
d5 = 2.00
n3 = 1.69979
.nu.3 = 555
r6 = 184.824
d6 = 0.20
r7 = 94.236
d7 = 9.13
n4 = 1.81265
.nu.4 = 25.4
r8 = -138.818
d8 = 1.22
r9 = 3090.860
d9 = 6.08
n5 = 1.49845
.nu.5 = 81.6
r10 = -91.089
d10 = 10.06
r11 = -417.889
d11 = 2.00
n6 = 1.81264
.nu.6 = 25.4
r12 = 46.330
d12 = 11.55
n7 = 1 49845
.nu.7 = 81.6
r13 = -222.307
d13 = 0.20
r14 = 81.468
d14 = 12.72
n8 = 1.60520
.nu.8 = 65.5
r15 = -74.895
d15 = 0.20
(aspherical
r16 = 45 554
d16 = 5.81
n9 = 1.73234
.nu.9 = 54.7
surface)
r17 = 98.609
d17 = variable
r18 = 35.274
d18 = 0.80
n10 = 1.88814
.nu.10 = 40.8
r19 = 13.894
d19 = 5.07
r20 = -52.577
d20 = 3.38
n11 = 1.79191
.nu.11 = 25.7
r21 = -13.945
d21 = 0.80
n12 = 1.82017
.nu.12 = 46.6
r22 = 32.430
d22 = 2.47
r23 = 25.717
d23 = 4.36
n13 = 1.62409
.nu.13 = 36.3
r24 = -26.590
d24 = 0.38
r25 = -22.907
d25 = 0.80
n14 = 1.83945
.nu.14 = 42.7
r26 = -272.680
d26 = variable
r27 = -27.753
d27 = 0.80
n15 = 1.77621
.nu.15 = 49.6
r28 = 70.696
d28 = 2.53
n16 = 1.85501
.nu.16 = 23.9
r29 = -194.277
d29 = variable
r30 = (stop)
d30 = 1.20
r31 = -329.251
d31 = 3.85
n17 = 1.52032
.nu.17 = 59.0
r32 = -33.663
d32 = 0.15
r33 = 109.721
d33 = 3.58
n18 = 1.50349
.nu.18 = 56.4
r34 = -67.095
d34 = 0.15
r35 = 48.472
d35 = 6.76
n19 = 1.50349
.nu.19 = 56.4
r36 = -32.464
d36 = 1.20
n20 = 1.82017
.nu.20 = 46.6
r37 = -305.379
d37 = 30.00
r38 = 81.431
d38 = 4.96
n21 = 1.51825
.nu.21 = 64.2
r39 = -42.735
d39 = 0.15
r40 = -133.745
d40 = 1.20
n22 = 1.88814
.nu.22 = 40.8
r41 = 22.914
d41 = 5.85
n23 = 1.51825
.nu.23 = 64.2
r42 = -473.752
d42 = 0.15
r43 = 273.136
d43 = 6.04
n24 = 1.55099
.nu.24 = 45.8
r44 = -22.885
d44 = 1.20
n25 = 1.81265
.nu.25 = 25.4
r45 = -66.890
d45 = 0.15
r46 = 41.727
d46 = 5.09
n26 = 1.58482
.nu.26 = 40.8
r47 = -72.688
d47 = 5.00
r48 = .infin.
d48 = 30.00
n27 = 1.60718
.nu.27 = 38.0
r49 = .infin.
d49 = 16.20
n28 = 1.51825
.nu.28 = 64.1
r50 = .infin.
__________________________________________________________________________
TABLE 2
______________________________________
Variable Focal length
spacing 5.50 9.39 13.75 42.08
46.75
______________________________________
d17 0.69 14.38 21.83 35.99
36.84
d26 40.24 24.10 15.34 3.80 3.99
d29 1.00 3.44 4.75 .nu.2.14
1.10
______________________________________
aspherical surface shape
surface R3
reference spherical
aspherical
surface R = -665.567
amount (R3)
h .DELTA.
aspherical surface
70% (20.09 mm) 87.8 .mu.m
coefficient 90% (25.83 mm) 227.1 .mu.m
k = 2.230 .times. D.sup.0
100% (28.70 mm) 336.3 .mu.m
B = 6.085 .times. D.sup.-7
aspherical
C = -2.254 .times. D.sup.-10
amount (R16)
h .DELTA.
D = 1.616 .times. D.sup.-13
70% (18.31 mm) 33.5 .mu.m
E = -6.431 .times. D.sup.-17
90% (23.54 mm) 112.4 .mu.m
surface R16 100% (26.16 mm) 198.1 .mu.m
reference spherical
zoom parameter
surface R = 45.554
fw/IS = 0.5
aspherical surface
hw/ht = 1.763
coefficient
hw/hz = 1.162
k = -1.901 .times. D.sup.2
.DELTA..nu.11n-.DELTA..nu.11p = 28.12
B = -2.116 .times. D.sup.-7
f13/f1 = 1.67
C = -1.366 .times. D.sup.-10
D = -2.652 .times. D.sup.-14
E = -2.143 .times. D.sup.-16
______________________________________
__________________________________________________________________________
(Numerical Value Embodiment 3)
f = 5.2 to 46.8 fno = 1.8 to 2.1 2w = 93.2.degree. to
__________________________________________________________________________
13.4.degree.
(aspherical
r1 = 133.567
d1 = 2.50
n1 = 1.77621
.nu.1 = 49.6
surface)
r2 = 31.225
d2 = 17.75
r3 = -1863.383
d3 = 2.00
n2 = 1.73234
.nu.2 = 547
r4 = 84.678
d4 = 9.01
r5 = -140.200
d5 = 2.00
n3 = 1.73234
.nu.3 = 547
r6 = 214.253
d6 = 0.20
r7 = 91.689
d7 = 10.05
n4 = 1.81255
.nu.4 = 25.4
r8 = -107.116
d8 = 1.20
r9 = 972.680
d9 = 6.53
n5 = 1.48915
.nu.5 = 70.2
r10 = -84.575
d10 = 10.05
r11 = -330.168
d11 = 2.00
n6 = 1.81264
.nu.6 = 25.4
r12 = 42.954
d12 = 10.95
n7 = 1.49845
.nu.7 = 81.6
r13 = -143.390
d13 = 0.20
r14 = 80.802
d14 = 10.00
n8 = 1.60520
.nu.8 = 65.5
r15 = -74.791
d15 = 0.20
r16 = 46.624
d16 = 4.41
n9 = 1.73234
.nu.9 = 547
r17 = 89.951
d17 = variable
r18 = 36.638
d18 = 0.80
n10 = 1.88814
.nu.10 = 40.8
r19 = 13.780
d19 = 5.02
r20 = -46.148
d20 = 0.80
n11 = 1.83945
.nu.11 = 42.7
r21 = 32.757
d21 = 2.78
r22 = 27.332
d22 = 4.18
n12 = 1.79191
.nu.12 = 25.7
r23 = -33.589
d23 = o.49
r24 = -25.382
d24 = 0.80
n13 = 1.82017
.nu.13 = 46.6
r25 = 450.224
d25 = variable
r26 = -29.318
d26 = 0.80
n14 = 1.77621
.nu.14 = 49.6
r27 = 57.089
d27 = 2.44
n15 = 1.85501
.nu.15 = 23.9
r28 = -267.542
d28 = variable
r29 = (stop)
d29 = 1.20
r30 = -345.052
d30 = 3.71
n16 = 1.50014
.nu.16 = 65.0
r31 = -33.307
d31 = 0.15
r32 = 108.966
d32 = 3.40
n17 = 1.50349
.nu.17 = 56.4
r33 = -66.285
d33 = 0.15
r34 = 46.492
d34 = 6.34
n18 = 1.50349
.nu.18 = 56.4
r35 = -32.104
d35 = 1.20
n19 = 1.82017
.nu.19 = 46.6
r36 = -525.239
d36 = 30.00
r37 = 157.757
d37 = 4.29
n20 = 1.51825
.nu.20 = 64.2
r38 = -36.928
d38 = 0.15
r39 = -92.667
d39 = 1.20
n21 = 1.88814
.nu.21 = 40.8
r40 = 21.383
d40 = 5.98
n22 = 1.51825
.nu.22 = 64.2
r41 = -123.919
d41 = 0.15
r42 = 148.278
d42 = 6.42
n23 = 1.55099
.nu.23 = 45.8
r43 = -19.560
d43 = 1.20
n24 = 1.81265
.nu.24 = 25.4
r44 = -85.685
d44 = 0.15
r45 = 56.956
d45 = 5.20
n25 = 1.65223
.nu.25 = 33.8
r46 = -41.016
d46 = 5.00
r47 = .infin.
d47 = 30.00
n26 = 1.60718
.nu.26 = 38.0
r48 = .infin.
d48 = 16.20
n27 = 1.51825
.nu.27 = 64.1
r49 = .infin.
__________________________________________________________________________
TABLE 3
______________________________________
Variable Focal length
spacing 5.20 9.01 13.00 40.11
46.80
______________________________________
d17 0.67 14.54 21.64 35.73
36.91
d25 38.97 22.67 14.50 4.79 5.56
d28 3.60 6.03 7.10 2.71 0.77
______________________________________
aspherical surface shape
surface R1
reference spherical
aspherical
surface R = 133.567
amount (R1)
h .DELTA.
aspherical surface
70% (29.63 mm) 192.8 .mu.m
coefficient
90% (33.33 mm) 525.5 .mu.m
k = 7.994 .times. D.sup.0
100% (37.04 mm) 805.2 .mu.m
B = -1.640 .times. D.sup.-8
C = -6.238 .times. D.sup.-11
D = -5.429 .times. D.sup.-14
E = -3.622 .times. D.sup.-17
zoom parameter
fw/IS = 0.473
hw/ht = 3.358
hw/hz = 1.352
.DELTA..nu.11n-.DELTA..nu.11p = 27.56
f13/f1 = 1.829
.DELTA..nu.13p-.DELTA..nu.13 n = 41.83
______________________________________
__________________________________________________________________________
(Numerical Value Embodiment 4)
f = 5.0 to 50.0 fno +1.8 to 2.4 2w = 95.5.degree. to
__________________________________________________________________________
12.6.degree.
(aspherical
r1 = 162.851
d1 = 2.50
n1 = 1.77621
.nu.1 = 49.6
surface)
r2 = 29.732
d2 = 17.75
r3 = 524.648
d3 = 2.00
n2 = 1.73234
.nu.2 = 54.7
r4 = 95.860
d4 = 9.01
r5 = -109.529
d5 = 2.00
n3 = 1.73234
.nu.3 = 547
r6 = 160.248
d6 = 0.20
r7 = 87.644
d7 = 10.05
n4 = 1.81265
.nu.4 = 254
r8 = -96.083
d8 = 1.20
r9 = -269.902
d9 = 6.53
n5 = 1.48915
.nu.5 = 70.2
r10 = -82.572
d10 = 10.05
r11 = -715.456
d11 = 2.00
n6 = 1.81264
.nu.6 = 25.4
r12 = 39.051
d12 = 10.95
n7 = 1.49845
.nu.7 = 81.6
r13 = -140.417
d13 = 0.20
r14 = 60.043
d14 = 10.00
n8 = 1.60520
.nu.8 = 65.5
r15 = -77.752
d15 = 0.20
(aspherical
r16 = 49.302
d16 = 4.41
n9 = 1.73234
.nu.9 = 54.7
surface)
r17 = 83.409
d17 = variable
r18 = 39.705
d18 = 0.80
n10 = 1.88814
.nu.10 = 40.8
r19 = 12.495
d19 = 5.02
r20 = -48.511
d20 = 0.80
n11 = 1.83945
.nu.11 = 42.7
r21 = -14.391
d21 = 2.78
r22 = 39.562
d22 = 4.18
n12 = 1.79191
.nu.12 = 25.7
r23 = 25.121
d23 = 0.49
r24 = -37.281
d24 = 0.80
n13 = 1.82017
.nu.13 = 46.6
r25 = -32.103
d25 = variable
r26 = -303.277
d26 = 0.80
n14 = 1.77821
.nu.14 = 49.6
r27 = -28.949
d27 = 2.44
n15 = 1.85501
.nu.15 = 23.9
r28 = 87.087
d28 = variable
r29 = -151.301
d29 = 1.20
r30 = (stop)
d30 = 3.71
n16 = 1.50014
.nu.16 = 65.0
r31 = 249400.578
d31 = 0.15
r32 = -42.665
d32 = 3.40
n17 = 1.50349
.nu.17 = 56.4
r33 = 77.871
d33 = 0.15
r34 = -89.166
d34 = 6.34
n18 = 1.50349
.nu.18 = 56.4
r35 = 41.440
d35 = 1.20
n19 = 1.82017
.nu.19 = 46.6
r36 = -35.591
d36 = 30.00
r37 = 861.801
d37 = 4.29
n20 = 1.51825
.nu.20 = 64.2
r38 = -37.509
d38 = 0.15
r39 = -28.353
d39 = 1.20
n21 = 1.88814
.nu.21 = 40.8
r40 = 131.469
d40 = 5.98
n22 = 1.51825
.nu.22 = 64.2
r41 = 17.313
d41 = 0.15
r42 = -109.752
d42 = 6.42
n23 = 1.55099
.nu.23 = 45.8
r43 = 120.858
d43 = 1.20
n24 = 1.81265
.nu.24 = 25.4
r44 = -20.584
d44 = 0.15
r45 = -96.935
d45 = 5.20
n25 = 1.65223
.nu.25 = 33.8
r46 = 44.259
d46 = 5.00
r47 = -30.190
d47 = 30.00
n26 = 1.60718
.nu.26 = 38.0
r48 = .infin.
d48 = 16.20
n27 = 1.51825
.nu.27 = 64.1
r49 = .infin.
d49 =
r50 = .infin.
__________________________________________________________________________
TABLE 4
______________________________________
Variable Focal length
spacing 5.00 8.89 12.50 37.50
50.00
______________________________________
d17 0.65 15.07 21.58 35.32
37.36
d26 36.66 19.53 12.05 3.72 6.11
d29 6.50 9.21 10.18 4.77 0.34
______________________________________
aspherical surface shape
surface R1
reference spherical
aspherical
surface R = 162.851
amount (R1)
h .DELTA.
aspherical surface
70% (25.74 mm) 360.2 .mu.m
coefficient
90% (33.10 mm) 936.9 .mu.m
k = 1.291 .times. D.sup.1
100% (36.78 mm) 1400.6 .mu.m
B = 4.732 .times. D.sup.-7
aspherical
C = -9.614 .times. D.sup.-11
amount (R16)
h .DELTA.
D = -1.173 .times. D.sup.-13
70% (15.85 mm) 22.4 .mu.m
E = -5.468 .times. D.sup.-18
90% (20.37 mm) 76.2 .mu.m
surface R16
100% (22.64 mm) 135.5 .mu.m
reference spherical
zoom parameter
fw/IS = 0.454
hw/ht = 3.561
hw/hz = 1.383
.DELTA..nu.11n-.DELTA..nu.11p = 25.86
f13/f1 = 1.82
______________________________________
According to the present invention, as described above, there can be
achieved a so-called four-unit zoom lens in which the lens disposition of
a fore lens unit, the lens disposition of a variator, a focusing system,
etc. are appropriately set, and when the maximum incidence height of the
on-axis light beam is ht and the incidence height of the off-axis light
beam of a maximum angle of view at the wide angle end is hw and the
incidence height of the off-axis light beam of a maximum angle of view at
a zoom position at a variable power ratio Z.sup.1/4 is hz, an aspherical
surface is provided on at least one surface in the fore lens unit which
satisfies 1.65<hw/ht and 1.15<hw/hz, whereby the distortion near the wide
angle end is corrected and further the changing of astigmatism, coma and
chromatic aberration resulting from a focal length change are corrected in
a well-balanced manner and which has high optical performance over the
entire variable power range and has an F number on the order of 1.8 at the
wide angle end, a wide angle end angle of view 2.omega.=90.degree. to
96.degree., a large aperture of a variable power ratio of the order of 8.5
to 10 and a wide angle and a high variable power ratio.
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